Add support for @Transactional in native images

This commit introduces a TransactionBeanRegistrationAotProcessor
in charge of creating the required proxy and reflection hints
when @Transactional is detected on beans.

It also refines DefaultAopProxyFactory to throw an exception
when a subclass-based proxy is created in native images
since that's unsupported for now (see gh-28115 related issue).

Closes gh-28717

spring-tx/src/main/resources/META-INF/spring/aot.factories

@@ -0,0 +1,2 @@
+org.springframework.beans.factory.aot.BeanRegistrationAotProcessor=\
+org.springframework.transaction.annotation.TransactionBeanRegistrationAotProcessor